Climb prop at high altitude cruise?

[DMD3.]

I overheard a conversation yesterday at the FBO where a guy who owns a Piper Cherokee likes to cruise at around 10-11k feet on X/C’s, and I heard him say that he actually prefers a climb prop over a cruise prop, as the extra RPMs due to the finer pitch helps him maintain thrust at that altitudes. He did say that if he got to where he spent most of his time flying at 5-6k feet and at lighter loads, he’d put a cruise prop back on his airplane. But at around 10k feet and with passengers, he claimed that his top-end performance was no worse than what it was when he had a cruise prop, and that having that prop was only a disadvantage, as it slowed his climb and therefore put extra wear on the engine.

The guy was casually chatting with several other pilots, and I didn’t stop to interrupt. I didn’t hear him mention what the horsepower of his Cherokee was, and he seemed like a fun person to talk with, but it’s just say-so from one person. But it definitely gives food for thought. So for those of you who have flown Cherokee, Skyhawk, or even a Cheetah/Tiger (perhaps even ESPECIALLY a Cheetah/Tiger) with both types of props and could compare the two, how true would you say this is? Could a climb prop potentially give the same top end performance if you climb to a high enough altitude?

I realize that if one spends a lot of time at those altitudes, then they may consider converting to a CS prop or just a different aircraft altogether, but I digress.

 

[kaiser]

I fly a Cessna 170 (O-300) with a cruise prop and I really don't like take offs some days. But in cruise - I feel like it's on the faster side on the book numbers, FWIW.

 

[dmspilot]

I overheard a conversation yesterday at the FBO where a guy who owns a Piper Cherokee likes to cruise at around 10-11k feet on X/C’s, and I heard him say that he actually prefers a climb prop over a cruise prop, as the extra RPMs due to the finer pitch helps him maintain thrust at that altitudes. He did say that if he got to where he spent most of his time flying at 5-6k feet and at lighter loads, he’d put a cruise prop back on his airplane. But at around 10k feet and with passengers, he claimed that his top-end performance was no worse than what it was when he had a cruise prop, and that having that prop was only a disadvantage, as it slowed his climb and therefore put extra wear on the engine.

The guy was casually chatting with several other pilots, and I didn’t stop to interrupt. I didn’t hear him mention what the horsepower of his Cherokee was, and he seemed like a fun person to talk with, but it’s just say-so from one person. But it definitely gives food for thought. So for those of you who have flown Cherokee, Skyhawk, or even a Cheetah/Tiger (perhaps even ESPECIALLY a Cheetah/Tiger) with both types of props and could compare the two, how true would you say this is? Could a climb prop potentially give the same top end performance if you climb to a high enough altitude?

I realize that if one spends a lot of time at those altitudes, then they may consider converting to a CS prop or just a different aircraft altogether, but I digress.

Cruise props are cruise props for efficiency, not necessarily for speed. At full throttle, the climb prop is capable of higher RPM and a higher top speed. The cruise prop will deliver a higher top speed only if the climb prop causes overspeeding.

 

[Llewtrah381]

Mine came pitched for climb and I found I frequently had issues keeping it below red line at altitude so I had it repitched to cruise. That helped tremendously with avoiding redline but added a few degrees to CHT. It did increase my cruise speed a few knots but didn’t hurt my climb performance much. Warrior with a 180HP.

 

[Clip4]

I overheard a conversation yesterday at the FBO where a guy who owns a Piper Cherokee likes to cruise at around 10-11k feet on X/C’s, and I heard him say that he actually prefers a climb prop over a cruise prop, as the extra RPMs due to the finer pitch helps him maintain thrust at that altitudes. He did say that if he got to where he spent most of his time flying at 5-6k feet and at lighter loads, he’d put a cruise prop back on his airplane. But at around 10k feet and with passengers, he claimed that his top-end performance was no worse than what it was when he had a cruise prop, and that having that prop was only a disadvantage, as it slowed his climb and therefore put extra wear on the engine.

The guy was casually chatting with several other pilots, and I didn’t stop to interrupt. I didn’t hear him mention what the horsepower of his Cherokee was, and he seemed like a fun person to talk with, but it’s just say-so from one person. But it definitely gives food for thought. So for those of you who have flown Cherokee, Skyhawk, or even a Cheetah/Tiger (perhaps even ESPECIALLY a Cheetah/Tiger) with both types of props and could compare the two, how true would you say this is? Could a climb prop potentially give the same top end performance if you climb to a high enough altitude?

I realize that if one spends a lot of time at those altitudes, then they may consider converting to a CS prop or just a different aircraft altogether, but I digress.

Gotta love bull poop.

Check some Cherokee and Tiger POHs.

From 10,000 - 12,500 ISA the full throttle OEM prop RPM is 2600 to 2700 rpm. The red line is 2700

The manufactures aren’t stupid. If they could put a prop on the plane so it climbed faster and cruised faster at a higher altitude, they would have done it.

 

[flyingron]

I'm not sure how the altitude factors into it. Yes you're going faster at higher altitude because the TAS works out faster, but the load on the prop is the same.

Think about it when flying constant speed. You can go faster balls to the wall but you will be more efficient with the RPMs dialed down.

 

[RyanB]

I heard him say that he actually prefers a climb prop over a cruise prop, as the extra RPMs due to the finer pitch helps him maintain thrust at that altitudes. He did say that if he got to where he spent most of his time flying at 5-6k feet and at lighter loads, he’d put a cruise prop back on his airplane. But at around 10k feet and with passengers, he claimed that his top-end performance was no worse than what it was when he had a cruise prop, and that having that prop was only a disadvantage, as it slowed his climb and therefore put extra wear on the engine.

Somebody has a lack of understanding. There is also no added wear on the engine between a cruise or climb prop.

 

[nrpetersen]

probably would drive around never getting above 2nd gear.

 

[Clip4]

Somebody has a lack of understanding. There is also no added wear on the engine between a cruise or climb prop.

Arguably there is more wear on the engine with a climb prop because the engine is running more RPM for a given airspeed.

 

[Daleandee]

Somebody has a lack of understanding. There is also no added wear on the engine between a cruise or climb prop.

Likely not a concern in this particular scenario but an article I read years ago (can't find the reference now) about H.A.L.T. research of aircraft engines proved that letting an engine spin a little faster was better than putting it under more load.

 

[FastEddieB]

probably would drive around never getting above 2nd gear.

A reference to this song, perhaps?

 

[FastEddieB]

Arguably there is more wear on the engine with a climb prop because the engine is running more RPM for a given airspeed.

You can argue that, but within normal operating range there’s no direct correlation between RPM and wear.

 

[hindsight2020]

Somebody has a lack of understanding. There is also no added wear on the engine between a cruise or climb prop.

Lost cause. This is the same demographic that legitimately believes pulling power low to the ground and climbing at 25/25 extends powerplant longevity to one entire overhaul's TBO worth of difference... while only operating a vented-crankcase engine at a pathetic fraction of the yearly use it'd take you to even reach TBO at OEM recommender calendar time.

 

[DMD3.]

Arguably there is more wear on the engine with a climb prop because the engine is running more RPM for a given airspeed.

I think the idea was the extra time spent in climb with a cruise prop, particularly when loaded, was harder on the engine. But higher RPMs makes sense.

 

[Dan Thomas]

Arguably there is more wear on the engine with a climb prop because the engine is running more RPM for a given airspeed.

RPM isn't the only factor. A coarser prop lowers the RPM but results in higher cylinder pressures, putting more load on the bearings.

 

[Clip4]

RPM isn't the only factor. A coarser prop lowers the RPM but results in higher cylinder pressures, putting more load on the bearings

At the cam, the rockers, and the valve guides, each time metal moves against metal there is some wear. Load on the piston doesn’t change this. If this wasn’t true, you would never need to replace these items at overhaul due to wear.
There is less spark plug erosion running lower rpms.

Faster RPM equals greater piston speed which adds stress to items like wrist pins and bearings. This is especially true in aircraft engines because you have big bore and short stroke. The horsepower required at a given airspeed remains unchanged. High rpm conditions result in more stresses and wear than lower RPM for a given horsepower.

 

[Dan Thomas]

At the cam, the rockers, and the valve guides, each time metal moves against metal there is some wear. Load on the piston doesn’t change this.

I wasn't talking about the cam and lifters. I was talking about the piston putting more load on the bearings at lower RPM and higher MP, which generates higher cylinder pressures, and the the force of the piston is reacted through the bearings---all of the crankshaft main and journal bearings---and accelerates wear.

In mechanical engineering there is the PV phenomenon. Pressure times surface velocity. Plain bearings don't do well at low RPM and high pressures, as lubricants are forced out and metals meet. The slow rotation doesn't carry sufficient oil into the pressure area either. So the bearings fail. Many years ago when the majority of auto transmissions were manually shifted, some people wouldn't downshift to maintain engine RPM when climbing hills, and the RPM would fall, cylinder pressures rose as the throttle was opened further, and bearing failure was very common.

High rpm conditions result in more stresses and wear than lower RPM for a given horsepower.

Not necessarily. Engines are designed for certain cruising RPMs to minimize wear. Old American cars had engines that typically redlined well under 5000 RPM, and often cruised under 2000 RPM. Then the new Japanese cars started showing up, and they had smaller engines designed for higher redline and cruise RPMs. American drivers, conditioned to the old sixes and V8s, still shifted at the RPMs they were used to, overloaded the bearings, and blew up the engines.

Aircraft engines are designed to be operated at certain RPMs, and those power settings are in the POH. You will note that many aircraft engines can be cruised right up close to redline, and they go to TBO doing that.

Cruise chart for Cessna 172N:



You think Lycoming and Cessna would tell you to cruise at 2650 if it was going to shorten the life of the engine?

 

[Dana]

As a climb prop has less pitch than a cruise prop, you're going to get less thrust and thus airspeed at any given rpm. For any fixed pitch prop, there is one airspeed where it's most efficient. A cruise prop is optimized at cruise airspeed, and a climb prop at a somewhat slower airspeed (usually a compromise; a prop optimized for Vx or Vy would be a lousy performer at cruise speed). And since prop pitch is a geometrical thing, a prop optimized for a lower speed would perform even worse up high where TAS is higher.

 

[Dan Thomas]

The airframe manufacturers specify the propeller pitch so that in level flight, near sea level, the engine will reach redline at full throttle. This prevents over-revving, and uses all the available rated HP of the engine.

When breaking in new or overhauled engines, Lycoming wants the engine run for an hour at 75% power, then another hour with varying settings between 75 and 65%, then a half-hour at full rated HP according to the airframe manufacturer's instructions. For a 172, this was full-throttle, 2700 RPM, and I found that the prop pitch was perfect even at 6000 feet. As air density decreases with altitude and temperature, HP decreases, but so does drag, and it seems to be fairly well-balanced at normal altitudes.

Those 172s sure scooted at full throttle in level cruise.

The TCDS for aircraft with fixed-pitch props specify what propellers are certified to be on that airplane and engine.

This is from the 172M TCDS, and specifies the props for landplane versions. Seaplanes use different props and they're also listed.



Note two things: There are NO cruise or climb props mentioned, and the simple note that "For all operations, 2700 RPM" is the limit. For ALL operations, including cruise. The O-320-E2D does not have a five-minute max HP rating as is sometimes found on larger engines.

So if anyone has a prop pitched higher or lower than what is shown here (53"), and has no STC for it, the airplane is not legally airworthy. "7553" means 75" diameter and 53" pitch.

The seaplane props for a 172M:



Note the much lower pitch, to match the lower cruise with floats dragging at the airplane, and the larger diameter to get more efficiency in takeoff and climb. That 80" diameter wouldn't work with the airplane on wheels; the ground clearance would be too small.

 

[chemgeek]

The optimal fixed propeller pitch depends on several factors, including engine power, acceptable climb rates, and being able to allow for near maximal rpm at cruise.

The high-compression STC available for the Traveler (AA-5) and Cheetah (AA-5A) is illustrative. While the STC allows the engine to develop only an extra 10 HP or so, this has a dramatic impact on excess power available for climb and cruise. With the stock cruise propeller (57" pitch), an AA-5 will climb like a banshee with the extra 10 HP, but will hit max rpm (2700) before you run out of throttle at cruise, therefore sacrificing potential cruise speed. (It is also very easy to over speed the engine with this power/prop combination.) WIth the STC propeller (a 61" pitch clipped propeller), it will still climb better than the stock engine/stock propeller, but will just about make max rpm (2650) below 10,000 feet, and will run out of throttle before it hits max rpm above 10,000 feet. The extra 4" of pitch results in about a 3-4 knot increase in max cruise speed, or you can throttle back and cruise at stock speeds at less rpm. It is not as easy to overspeed this power/prop combination.

So yes, you can use a lower pitch prop and spin it faster (within max rpm limitations) to get the same airspeed as a higher pitch prop that can only run slower, (most Grummans gave you a choice of a climb or cruise prop configuration), but the faster you run the engine, the more internal friction you must overcome. The cruise prop can potentially propel the airplane faster and more efficiently in cruise at the cost of reduced climb.

 

[William Pete Hodges]

Cruise chart for Cessna 172N:

View attachment 129275

You think Lycoming and Cessna would tell you to cruise at 2650 if it was going to shorten the life of the engine?

This chart us a really good example of how engine power changes with altitude and RPM. Notice how the cruise RPM listed is less at lower altitude? That's because at higher RPM the engine would develop more power than its continuous power rating. That would be considered unsustainable, leading to shorter time to overhaul. At higher altitude the engine must turn more RPM to make enough power to cruise effectively.

I agree that as long as the RPM is kept below redline, the climb prop will give better performance at all altitudes because the engine will be turning faster and breathing more air.

 

[flyingron]

Arguably there is more wear on the engine with a climb prop because the engine is running more RPM for a given airspeed.

Total number of revolutions do not equate to wear. This is a myth that your engine only has a certain number of turns in it before it wears out.

Heat is what kills engines in practice.

 

[FastEddieB]

Total number of revolutions do not equate to wear. This is a myth that your engine only has a certain number of turns in it before it wears out.

This.

In normal operation, metal parts are not meeting - they are held apart by a thin film of oil. Evidenced by…

1) How quickly the engine destroys itself after the loss of oil pressure, when metal parts DO start meeting.

2) The fact that after thousands of hours of operation, hone marks may still be visible on cylinders.

One possible exception may be accessories not lubricated by engine oil. I’m specifically thinking of dry vacuum pumps, lubricated by graphite on their vanes. I can see how their life might be affected by rpm, though probably not enough in practice to matter.

 

[Dan Thomas]

Notice how the cruise RPM listed is less at lower altitude? That's because at higher RPM the engine would develop more power than its continuous power rating.

That Lycoming O-320 has a max continuous rating of 2700 RPM and 150 HP, straight out of the TCDS. As I posted:



And as I said, the propeller is pitched to allow full-throttle operation that gives 2700 RPM and 150 HP at sea level. No maximum continuous ratings are being exceeded.

Now, if we look at the TCDS for some of the Continental IO-520s, wee see this:



We see a max continuous rating there of 285 HP at 2700 RPM, and 300 HP at 2850 for five minutes at sea level. The POH charts for any airplane using these engines will reflect that. Big engines that make a lot more HP also make a lot more waste heat, and running them a max power for too long starts shortening the life of the engine. Note, too, that the 285 max continuous is at sea level and full throttle, 2700 RPM, so the prop has been dialed back.

One possible exception may be accessories not lubricated by engine oil. I’m specifically thinking of dry vacuum pumps, lubricated by graphite on their vanes. I can see how their life might be affected by rpm, though probably not enough in practice to matter.

It matters. Continental's pump gearing runs their pumps faster than Lycoming' pumps, and they wear out sooner. More speed means more friction and more heat.

Lycoming pump pads generally turn 1.3 times crankshaft speed. Continental pump pads turn 1.5 to 1.545 times crank speed.

From https://www.avweb.com/ownership/dry-vacuum-pumps/

 

[Clip4]

Total number of revolutions do not equate to wear. This is a myth that your engine only has a certain number of turns in it before it wears out.

Heat is what kills engines in practice.

That must be why they run engines as cool as possible - oh wait - they don’t

 

[Clip4]

I wasn't talking about the cam and lifters. I was talking about the piston putting more load on the bearings at lower RPM and higher MP, which generates higher cylinder pressures, and the the force of the piston is reacted through the bearings---all of the crankshaft main and journal bearings---and accelerates wear.

In mechanical engineering there is the PV phenomenon. Pressure times surface velocity. Plain bearings don't do well at low RPM and high pressures, as lubricants are forced out and metals meet. The slow rotation doesn't carry sufficient oil into the pressure area either. So the bearings fail. Many years ago when the majority of auto transmissions were manually shifted, some people wouldn't downshift to maintain engine RPM when climbing hills, and the RPM would fall, cylinder pressures rose as the throttle was opened further, and bearing failure was very common.

Not necessarily. Engines are designed for certain cruising RPMs to minimize wear. Old American cars had engines that typically redlined well under 5000 RPM, and often cruised under 2000 RPM. Then the new Japanese cars started showing up, and they had smaller engines designed for higher redline and cruise RPMs. American drivers, conditioned to the old sixes and V8s, still shifted at the RPMs they were used to, overloaded the bearings, and blew up the engines.

Aircraft engines are designed to be operated at certain RPMs, and those power settings are in the POH. You will note that many aircraft engines can be cruised right up close to redline, and they go to TBO doing that.

Cruise chart for Cessna 172N:

View attachment 129275

You think Lycoming and Cessna would tell you to cruise at 2650 if it was going to shorten the life of the engine?

Do you think Cessna could market slower aircraft? They have those high RPM values because people like airplanes that climb fast and go fast.

 

[Dan Thomas]

Do you think Cessna could market slower aircraft? They have those high RPM values because people like airplanes that climb fast and go fast.

They have those high RPMs because the propeller is a fussy device. At 700 RPM, idle RPM, it will barely move the airplane. Double that to 1400 and you get a really fast taxi. At 2100 RPM it will go fast but isn't going to take off. Add 700 more RPM, to 2800, and it will not only take off but climb respectably.

It's that last bit of the RPM range where flight happens. And it's because of physics: K = MV². Kinetic energy is equal to mass times velocity squared. We get roughly double the mass of air moved by the prop between 1400 and 2800, but we get, theoretically, four times the reaction (thrust) off the prop as the RPM doubles and the air velocity doubles.

And THAT's why no matter what engine you use, you will see propeller RPMs as high as possible without losing too much to drag at the tips as the tip speed gets close to Mach 1. Larger props have to turn slower because of that. The noisy airplanes, like a Cessna 185 with its 86-inch prop, is losing considerable HP to drag at 2850 RPM because it's so close to Mach 1, 729 MPH plus a bit for forward speed. Some pilots find that the airplane performs better and quieter if they pull the prop back to under 2800, where the losses to drag diminish and the extra pitch uses that HP instead.

 

[Dana]

That must be why they run engines as cool as possible - oh wait - they don’t

It would be more correct to say that excessive heat kills engines. You can't make an engine run cold, it's gonna heat up some, so you try to control it and pick a temperature where the engine components will be at their intended clearances after some amount of thermal expansion, and the oil has thinned appropriately. You don't want it too hot or too cold.

 

[FastEddieB]

It would be more correct to say that excessive heat kills engines.

Beat me to it!

 

[Daleandee]

Beat me to it!

One of the earliest things I was taught concerning IC engines was that its two greatest enemies were heat & dirt. Use good filters (fuel, oil, & air) and keep it cool.

Lycoming gives a minimum CHT for operation at 150ºF. Seems a good maximum is 380ºF. The middle of that range is 265ºF. Anyone even near the middle of the range?

 

[Dan Thomas]

Too little heat, and the engine will not produce rated horsepower, and it will use more fuel.

This is why cars have thermostats. Take that thermostat out and it will run a lot cooler, but performance suffers. The fuel does not atomize well in a cold engine, clearances are larger, and carbon forms much faster in the head and on the piston because it's not being burned off. Emissions from a cold engine are much worse.

Even boat engines have thermostats. They're using stone-cold water from the lake/river/ocean for cooling, not warm water from the "cold" end of the radiator. They could be run at 100°F or less if we wanted, but they don't run well there.

https://auto.howstuffworks.com/how-does-the-thermostat-in-a-cars-cooling-system-work.htm

 

[Daleandee]

Too little heat, and the engine will not produce rated horsepower, and it will use more fuel.

This is why cars have thermostats. Take that thermostat out and it will run a lot cooler, but performance suffers. The fuel does not atomize well in a cold engine, clearances are larger, and carbon forms much faster in the head and on the piston because it's not being burned off. Emissions from a cold engine are much worse.

Even boat engines have thermostats. They're using stone-cold water from the lake/river/ocean for cooling, not warm water from the "cold" end of the radiator. They could be run at 100°F or less if we wanted, but they don't run well there.

https://auto.howstuffworks.com/how-does-the-thermostat-in-a-cars-cooling-system-work.htm

I won't disagree with you but point out that most auto IC engines are set at 212ºF (the old standard was 180-195ºF) so 265ºF seems quite reasonable and is more than 100ºF above the minimum that Lycoming has set for their engines. So it seems that running an engine at 265ºF would be better than 380ºF.

I realize that auto and aircraft engines are not the same but if fuel burns efficently at 212ºF in autos it should burn very well at 265ºF in a Lycoming. FWIW

 

[Dan Thomas]

I won't disagree with you but point out that most auto IC engines are set at 212ºF (the old standard was 180-195ºF) so 265ºF seems quite reasonable and is more than 100ºF above the minimum that Lycoming has set for their engines. So it seems that running an engine at 265ºF would be better than 380ºF.

I realize that auto and aircraft engines are not the same but if fuel burns efficently at 212ºF in autos it should burn very well at 265ºF in a Lycoming. FWIW

Getting air cooling to keep temperatures down as low as 265°F would take a lot more finning of the heads and cylinders and more airflow. More weight, drag, engine size and everything.

The auto engine's liquid-cooling temps are based on the boiling point of the coolant. To keep it from boiling, the system has to be pressurized. We could design a liquid cooling system that ran at 265°F and maybe get better performance, but we'd need heavier radiator with thicker tubing, and heavier piping. More weight and cost, and heavier rad tubing slows the heat transfer, too, so maybe a bigger radiator would be necessary.

Depending on the source, I find that the vapor pressure of water at 265°F is around 750 PSI. You can see why we don't run liquid-cooled systems at that temperature even though it might be better.

Our machines are all a collection of compromises.

 

[Daleandee]

Our machines are all a collection of compromises.

 

[William Pete Hodges]

Notice how the cruise RPM listed is less at lower altitude? That's because at higher RPM the engine would develop more power than its continuous power rating.

>>>>>>>>>
Dan Thomas said:

"That Lycoming O-320 has a max continuous rating of 2700 RPM and 150 HP, straight out of the TCDS. As I posted:

And as I said, the propeller is pitched to allow full-throttle operation that gives 2700 RPM and 150 HP at sea level. No maximum continuous ratings are being exceeded"
>>>>>>>>>>

Dan, I don't fully agree with you if you are talking about cruising flight. Practically all of these engines are designed to operate full rich above 75% power. At or below 75% power it acceptable and desirable to lean to less than full rich for better economy in cruise. The difference in fuel used can be substantial. Airplane manufacturers know this and therefore do not normally publish cruise data at power settings that require a full rich mixture. When you look at the chart in my previous response, the highest power setting listed is 76%, and a properly leaned ROP engine at that setting will burn 8.6 or 8.5 GPH. At full rich it will burn about 12-13 GPH.

We know the real limiting factor here is temperature. As long as we can run continuously below 435°F CHT we should get acceptable engine life, but the lower the better as long as the oil temperature is maintained between 140-235°F, with 180-195°F being about ideal. My airplane climbs at about 400°F CHT and cruises with a CHT of about 325-350°F depending on power settings in cruise.

If you figure it takes 20-30 minutes at full power to climb at or near full rich, followed by 3-4 hours of continuous cruise at reduced power and leaned ROP, then I stand by my statement the engine is not rated for continuous rated power for the entire flight.

 

[Dan Thomas]

If you figure it takes 20-30 minutes at full power to climb at or near full rich, followed by 3-4 hours of continuous cruise at reduced power and leaned ROP, then I stand by my statement the engine is not rated for continuous rated power for the entire flight.

And yet, the TCDS for that engine says "for all operations, 2700 RPM, 150 HP." There is NO mention of any max continuous with that engine as there is with larger engines.

Climbing for 20 or 30 minutes at full throttle is not using either 2700 RPM with a fixed-pitch prop, as that RPM is only possible in level flight, nor is it producing anywhere near 150 HP once you get away from sea level even if the throttle is wide open. The POH will also tell you to lean as necessary for best RPM in extended climbs to higher altitudes. From the 172N POH:




From the Lycoming O-320 Operator's Manual we get the altitude performance chart. In all the Lyc O-320-E2D powered 172s I flew, I seldom saw any more than 2400 RPM in the climb:



At 3000 feet, at 2400 RPM, we're already down to 125 HP, or 83% power. At 5000, 78%. AT full-throttle level flight, 2700 RPM, at 8000 feet, we're getting 115 HP, or 77% power. This agrees with the 172N's cruise chart for 8000 feet:



2650 RPM, standard temp and pressure, at 8000 feet, is 75% power. That throttle is pretty much wide open.

 

[Domenick]

Power Performance Excel workbook corrected for density altitude. Easily adjustable for specific NA engines. Creates charts for printing and posting. PM me with questions, bugs, and b itches.

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